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FIGURE 8.9 Atmospheric carbon-dioxide measurements that have been collected continuously since 1958 at the Mauna Loa Observatory, Hawaii. The seasonal oscillation of carbon dioxide (CO2) reflects the relative photosynthesis [Eq. (1.1)] in the Northern and Southern Hemispheres associated with the breathing of the Earth system. During this half-century period, the global concentration of atmospheric carbon dioxide has been continuously increasing. Modified from Keeling and Whorf (2000).

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FIGURE 8.9 Atmospheric carbon-dioxide measurements that have been collected continuously since 1958 at the Mauna Loa Observatory, Hawaii. The seasonal oscillation of carbon dioxide (CO2) reflects the relative photosynthesis [Eq. (1.1)] in the Northern and Southern Hemispheres associated with the breathing of the Earth system. During this half-century period, the global concentration of atmospheric carbon dioxide has been continuously increasing. Modified from Keeling and Whorf (2000).

would have extracted carbon dioxide from the atmosphere through photosynthesis [Eq. (1.1)].

After remaining relatively constant for almost 10,000 years, global carbon dioxide concentrations have increased nearly 30% (from 280 to 365 parts per million) just since 1850 (Fig. 8.10), along with the geometric growth of the human population (Fig. II). Given the close historical relationship between global temperature and carbon dioxide concentrations throughout the past half-million years (Fig. 7.4), it appears that the dramatic increase in the volume of carbon dioxide in the atmosphere has contributed significantly to the 20th century being the warmest period in the past millennium.

What forces influence environmental variability over various space and time dimensions in the Earth system?

Despite these apparent relationships between global carbon dioxide concentrations and temperatures, it is important to recognize that there are other factors that contribute to global warming and that correlation does not mean causation. The role of water vapor through time, in particular, remains an enigma in understanding the dynamics of greenhouse gases that contribute to the Earth's heat budget.

In many ways, the relatively pristine nature of Antarctica acts as a sentinel of

TABLE 8.1 Principal Greenhouse Gases in the Earth Systems a

Gas

Atmospheric percentage 1850 1999

Atmospheric lifetime

Global warming potential b

Water vapor (H2O)

0 0

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